Apparatus and method for encoding and decoding moving picture using adaptive scanning

ABSTRACT

Provided is an apparatus and method for encoding/decoding a moving picture based on adaptive scanning. The moving picture apparatus and method can increase a compression rate based on adaptive scanning by performing intra prediction onto blocks of a predetermined size, and scanning coefficients acquired from Discrete Cosine Transform (DCT) of a residue signal and quantization differently according to the intra prediction mode. The moving picture encoding apparatus includes: a mode selector for selecting and outputting a prediction mode; a predictor for predicting pixel values of pixels to be encoded of an input video based on the prediction mode to thereby output a residue signal block; a transform/quantization unit for performing DCT onto the residue signal block and quantizing the transformed residue signal block; and an encoder for adaptively scanning and encoding the quantized residue signal block based on the prediction mode.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of application Ser. No. 13/910,639filed on Jun. 5, 2013, which is a continuation of application Ser. No.13/469,536 filed on May 11, 2012, now U.S. Pat. No. 8,520,729, which isa continuation of application Ser. No. 12/090,699 having a 371(c) dateof Apr. 18, 2008, now U.S. Pat. No. 8,199,819, which is a U.S. nationalstage application of International Application No. PCT/KR2006/004260filed on Oct. 19, 2006, which claims the benefit of Korean ApplicationNo. 10-2005-0099733 filed on Oct. 21, 2005, in the Korean IntellectualProperty Office. The entire disclosures of application Ser. Nos.13/910,639, 13/469,536, and 12/090,699, International Application No.PCT/KR2006/004260, and Korean Application No. 10-2005-0099733 areincorporated herein by reference for all purposes.

BACKGROUND

1. Field

The present invention relates to encoding and decoding of a movingpicture based on adaptive scanning; and, more particularly, to a movingpicture encoding/decoding apparatus that can increase a compression rateby performing intra prediction onto blocks of a predetermined size, andadaptively scanning coefficients acquired from Discrete Cosine Transform(DCT) of a residue signal and quantization differently according to theintra prediction mode, and a method thereof.

2. Description of Related Art

According to an H.264 standard arranged for encoding/decoding a movingpicture, the encoding/decoding is performed on the basis of a unit ofmacro blocks or a unit of a sub-block. One frame includes a plurality ofmacro blocks, and the sub-block is acquired by dividing a macro blockinto two or four sub-blocks. The encoding and decoding are carried outbased on temporal prediction and spatial prediction. Temporal predictionis predicting motion of the macro blocks of a current frame by referringto macro blocks of adjacent frames. Spatial prediction is predicting amacro block of a current frame to be encoded based on adjacent macroblocks within the current frame.

The spatial prediction is also referred to as intra prediction. Theintra predication takes advantage of a feature that adjacent pixels of apixel to be predicted is highly likely to have a similar value.According to the H.264 standard, a pixel value of a current block ispredicted based on a prediction mode considering nine directionalities.

FIG. 1 is a view showing an intra prediction mode for 4×4 blocks and 8×8blocks in the H.264 standard. There are nine prediction modes accordingto the prediction direction: a vertical mode (mode 0), a horizontal mode(mode 1), a DC mode (mode 2), a Diagonal Down Left mode (mode 3), aDiagonal Down Right mode (mode 4), a Vertical_Right mode (mode 5), aHorizontal_Down mode (mode 6), a Vertical_Left mode (mode 7), and aHorizontal_Up mode (mode 8). The arrows signify prediction directions.Hereinafter, a prediction process in the vertical mode and thehorizontal mode when intra prediction is performed onto 4×4 blocks willbe described.

FIG. 2 is a view for describing a pixel prediction process in thevertical mode performed onto 4×4 blocks 300. As shown in FIG. 2, pixelsa, e, i, and m 302, 304, 306 and 308 are predicted from an adjacentpixel A in the vertical direction. In the same way, pixels b, f, j and nare predicted from a pixel B, and pixels c, g, k and o are predictedfrom a pixel C, while pixels d, h, I and p are predicted from a pixel D.

FIG. 3 is a view for describing a pixel prediction process in thehorizontal mode performed onto 4×4 blocks 300. As shown in FIG. 3,pixels a, b, c and d 312, 314, 316 and 318 are predicted from anadjacent pixel I in the horizontal direction. In the same way, pixels e,f, g and h are predicted from a pixel J, and i, j, k and I are predictedfrom a pixel K pixels, while pixels m, n, o and p are predicted from apixel L.

Meanwhile, a conventional moving picture encoder performs entropyencoding by performing Discrete Cosine Transform (DCT) and quantizationonto a residue signal, which is obtained by differentially dividing apredicted signal and a current signal, to thereby produce coefficientsand performing zigzag scanning onto the coefficients.

However, the correlation of the residue signal is likely to be high in ahorizontal direction or a vertical direction according to whether theprediction mode is a horizontal mode or a vertical mode. Therefore, theconventional encoding method using a fixed zigzag scanning has adrawback that it is not appropriate for acquiring a high compressionrate.

SUMMARY

It is, therefore, an object of the present invention to provide a movingpicture encoding apparatus and method that can increase a compressionrate based on adaptive scanning by performing intra prediction ontoblocks of a predetermined size, and adaptively scanning coefficientsacquired from Discrete Cosine Transform (DCT) of a residue signal andquantization according to the intra prediction mode, and a decodingapparatus and method therefor.

In accordance with one aspect of the present invention, there isprovided an apparatus for encoding a moving picture based on adaptivescanning, which includes: a mode selecting means for selecting andoutputting a prediction mode; a predicting means for predicting pixelvalues of pixels to be encoded of an input video based on the predictionmode to thereby output a residue signal block; a transform/quantizationmeans for performing Discrete Cosine Transform (DCT) onto the residuesignal block and quantizing the transformed residue signal block; and anencoding means for adaptively scanning and encoding the quantizedresidue signal block based on the prediction mode.

In accordance with another aspect of the present invention, there isprovided an apparatus for decoding a moving picture based on adaptivescanning, which includes: an entropy decoder for receiving encodedbitstream, decoding the encoded bitstream based on an entropy decodingmethod, and outputting decoded signals; a scanning method detector forreceiving the decoded signals from the entropy decoder, acquiring ascanning method used in the encoding of the decoded signals, andoutputting the scanning method information along with the decodedsignals; and a video recovering unit for recovering the decoded signalsbased on the scanning method and outputting a recovered video, whereinthe scanning method is an adaptive scanning where different scanningmethods are applied based on an intra prediction mode.

In accordance with another aspect of the present invention, there isprovided a method for encoding a moving picture based on adaptivescanning, which includes the steps of: a) selecting a prediction mode;b) predicting pixel values of pixels to be encoded of an input videobased on the selected prediction mode and outputting a residue signalblock; c) performing Discrete Cosine Transform (DCT) onto the residuesignal block and quantizing the transformed residue signal block; d)adaptively scanning the quantized residue signal block based on theprediction mode and outputting scanned coefficients; and e) encoding thescanned coefficients.

The present invention can improve an encoding compression rateremarkably by performing intra prediction onto blocks of a predeterminedsize, and adaptively scanning coefficients acquired from Discrete CosineTransform (DCT) of a residue signal and quantization differentlyaccording to the intra prediction mode, and a method thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of the preferredembodiments given in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a view showing an intra prediction mode for 4×4 blocks and 8×8blocks in the H.264 standard;

FIG. 2 is a view describing a pixel prediction process in a verticalmode;

FIG. 3 is a view describing a pixel prediction process in a horizontalmode;

FIG. 4 is a block view illustrating a moving picture encoding apparatusin accordance with an embodiment of the present invention;

FIG. 5 is a view showing a conventional zigzag scanning;

FIG. 6 is a view showing a horizontal preference scanning in accordancewith an embodiment of the present invention;

FIG. 7 is a view showing a vertical preference scanning in accordancewith an embodiment of the present invention;

FIG. 8 is a flowchart describing a moving picture encoding method usingadaptive scanning in accordance with an embodiment of the presentinvention;

FIG. 9 is a flowchart describing an adaptive scanning in accordance withan embodiment of the present invention; and

FIG. 10 is a block view illustrating a moving picture decoding apparatusin accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The following description exemplifies only the principles of the presentinvention. Even if they are not described or illustrated clearly in thepresent specification, one of ordinary skill in the art can embody theprinciples of the present invention and invent various apparatuseswithin the concept and scope of the present invention. The use of theconditional terms and embodiments presented in the present specificationare intended only to make the concept of the present inventionunderstood, and they are not limited to the embodiments and conditionsmentioned in the specification.

In addition, all the detailed description on the principles, viewpointsand embodiments and particular embodiments of the present inventionshould be understood to include structural and functional equivalents tothem. The equivalents include not only currently known equivalents butalso those to be developed in future, that is, all devices invented toperform the same function, regardless of their structures.

Functions of various devices illustrated in the drawings including afunctional block expressed as a processor or a similar concept can beprovided not only by using hardware dedicated to the functions, but alsoby using hardware capable of running proper software for the functions.When a function is provided by a processor, the function may be providedby a single dedicated processor, single shared processor, or a pluralityof individual processors, part of which can be shared.

The apparent use of a term, ‘processor’, ‘control’ or similar concept,should not be understood to exclusively refer to a piece of hardwarecapable of running software, but should be understood to include adigital signal processor (DSP), hardware, and ROM, RAM and non-volatilememory for storing software, implicatively. Other known and commonlyused hardware may be included therein, too.

Other objects and aspects of the invention will become apparent from thefollowing description of the embodiments with reference to theaccompanying drawings. When it is thought that a detailed description ofa prior art feature may obscure the points of the invention, thedescription will not be provided herein. Herein, preferred embodimentsof the present invention will be described in detail with reference tothe accompanying drawings.

FIG. 4 is a block view illustrating a moving picture encoding apparatusin accordance with an embodiment of the present invention.

As shown in FIG. 4, the moving picture encoding apparatus includes anintra predictor 110, a mode selector 120, a Discrete Cosine Transform(DCT)/quantization unit 130, and an entropy encoder 140.

The mode selector 120 selects an optimal prediction mode among theaforementioned intra prediction modes and outputs it to the intrapredictor 110. In other words, the mode selector 120 selects one amongdiverse encoding prediction modes available during 4×4 intra prediction,16×16 intra prediction and 8×8 intra prediction. Generally, it selectsone prediction mode based on rate-distortion optimization.

In case of luminance blocks, the prediction modes include a verticalmode, a horizontal mode, a DC mode, a Diagonal_Down_Left mode, aDiagonal_Down_Right mode, a Vertical_Right mode, a Horizontal_Down mode,a Vertical_Left mode, and a Horizontal_Up mode, which are intra 4×4luminance encoding modes of the H.264 standard, and a vertical mode, ahorizontal mode, a plane mode and a DC mode, which are intra 16×16luminance encoding modes.

With respect to chrominance blocks, the prediction modes include avertical mode, a horizontal mode, a plane mode and a DC mode, which areintra M×N chrominance encoding modes of the H.264 standard.

The intra predictor 110 performs prediction on an input image accordingto the prediction mode inputted from the mode predictor 120 and outputsa residue signal block which represents a difference between the pixelvalue of a macro block of a current frame to be encoded and a predictedpixel value. In the present embodiment, 4×4 intra prediction isperformed onto the pixels of a luminance block, and 8×8 intra predictionis performed onto the pixels of a chrominance block.

The DCT/quantization unit 130 performs DCT and quantization onto theresidue signal block inputted from the intra predictor 110 and outputsit to the entropy encoder 140.

The entropy encoder 140 arranges coefficients by adaptively scanning thequantized residue signal block regardless of the kind of the predictionmode, performs entropy encoding, and outputs encoded signals. Theentropy encoding is an encoding method which increases the datacompression rate by allocating a few bits to data with a high occurrencefrequency number and many bits to data with a low occurrence frequencynumber. The entropy encoding that may be applied to the presentinvention includes context adaptive variable length coding (CAVLC) andcontext-based adaptive binary arithmetic coding (CABAC).

FIG. 5 is a view describing a conventional zigzag scanning. Theconventional zigzag scanning of FIG. 5 is devised in consideration thatsignificant coefficients of the DCT are highly likely to be positionedin the left upper part. However, when the vertical mode or a horizontalmode is selected as an intra prediction mode, the correlation propertyof the residue signal may increase in a vertical or a horizontaldirection. In the case of the vertical mode, the significantcoefficients mainly appear in a first row or so. And, in the case of thehorizontal mode, the significant coefficients mainly appear in a firstcolumn or so. Therefore, another scanning method that can replace theconventional zigzag scanning is required. Hereinafter, embodiments ofadaptive scanning will be described according to the kinds of the intraprediction mode.

FIG. 6 is a view showing a horizontal preference scanning in accordancewith an embodiment of the present invention, and FIG. 7 is a viewshowing a vertical preference scanning in accordance with an embodimentof the present invention.

According to the embodiment of the present invention, the entropyencoder 140 uses the horizontal preference scanning method shown in FIG.6 when the intra prediction mode is a vertical mode. When the intraprediction mode is a horizontal mode, the entropy encoder 140 uses thevertical preference scanning method shown in FIG. 7. In the other cases,the entropy encoder 140 uses the conventional zigzag scanning, arrangescoefficients, performs entropy encoding, and outputs encoded signals.

According to the horizontal preference scanning method illustrated inFIG. 6, all the blocks of the first row are scanned and then thesubsequent scanning is performed in a sequence from all the blocks ofthe first row, followed by the first to third blocks in the second row,the second block and the first block in the third row, the first andsecond blocks in the fourth row, the third block in the third row, thefourth block in the second row, the fourth block in the third row, andthe third and fourth blocks in the fourth row. Therefore, since thehorizontal preference scanning of the present invention scans all theblocks in the first row prior to the other rows, it has a highcorrelation in the row direction and it is appropriate for the verticalmode where the significant coefficients are mainly positioned in thefirst row or so.

According to the vertical preference scanning described in FIG. 7,scanning is performed in a sequence from all the blocks in the firstcolumn first, followed by the first to third blocks in the secondcolumn, the second block and the first block in the third column, thefirst and second blocks in the fourth column, the third block in thethird column, the fourth block in the second column, the fourth block inthe third column, and the third and fourth blocks in the fourth column.Therefore, the vertical preference scanning of the present invention hasa high correlation in the column direction and it is appropriate for thevertical mode where the significant coefficients are mainly positionedin the first column or so.

Since the present invention determines the scanning method to be appliedbased on the intra mode, it scarcely affects the existing syntax and theapparatus of the present invention can be realized by applying a littlemodification to the semantics of a scanning method in the encoding anddecoding. Since those skilled in the art of a moving pictureencoding/decoding technology such as the H.264 standard can easilyrealize the adaptive scanning based on an intra prediction mode, whichis suggested in the present invention, detailed description on it willnot be provided herein.

FIG. 8 is a flowchart describing a moving picture encoding method usingadaptive scanning in accordance with an embodiment of the presentinvention.

First, when an image to be encoded is inputted to the intra predictor110 at step S510, the mode selector 120 selects an intra prediction modeat step S520.

Subsequently, the intra predictor 110 performs prediction onto theinputted image based on the selected prediction mode at step S530, andcreates a residue signal block having a difference value between a pixelvalue in a macro block of a current frame to be encoded and a predictedpixel value at step S540.

At step S550, the DCT/quantization unit 130 performs DCT onto theresidue signal block and quantizes the transformed residue signal block.

Subsequently, the entropy encoder 140 adaptively scans the quantizedresidue signal block based on the prediction mode at step S560, performsentropy encoding onto the scanned coefficients, and outputs theentropy-encoded coefficients at step S570.

FIG. 9 is a flowchart describing an adaptive scanning in accordance withan embodiment of the present invention. First, it is determined at stepS610 whether the prediction mode is a vertical mode. When it isdetermined that the prediction mode is the vertical mode, horizontalpreference scanning is performed at step S620. Meanwhile, when theprediction mode is not the vertical mode, it is determined at step S630whether the prediction mode is a horizontal mode.

When the prediction mode is the horizontal mode, vertical preferencescanning is carried out at step S640. When it is not the horizontalmode, zigzag scanning is carried out at step S650.

FIG. 10 is a block view illustrating a moving picture decoding apparatusin accordance with an embodiment of the present invention.

As illustrated in FIG. 10, the moving picture decoding apparatus of thepresent invention includes an entropy decoder 210, a scanning methoddetector 220, and an image recovery unit 230.

The entropy decoder 210 receives an encoded bitstream and decodes it byusing an entropy decoding method such as Context Adaptive VariableLength Coding (CAVLC) and Context-based Adaptive Binary ArithmeticCoding (CABAC).

The scanning method detector 220 receives the decoded signal from theentropy decoder 210, acquires information on how the decoded signal wasscanned in the encoding process, and transmits the scanning methodinformation to the image recovery unit 230 along with the decodedsignal.

The image recovery unit 230 recovers the decoded signal based on thescanning method and outputs a recovered image.

TABLE 1 Con- Fore- News tainer man Silent Paris Mobile Tempete (QCIF)(QCIF) (QCIF) (QCIF) (CIF) (CIF) (CIF) Entire 100 100 100 100 100 100100 Frame (30 (30 (30 (35 (30 (30 (30 Hz) Hz) Hz) Hz) Hz) Hz) Hz) Con-CABAC, Intra only (Intra 4 × 4 mode), dition QP (25, 30, 35, 40)

As shown in the Table 1, seven images of different sizes were tested.

The following Table 2 compares compression rates, when the test imagesare encoded based on the encoding method using the adaptive scanning andthe conventional encoding method using the H.264 zigzag scanning underthe aforementioned experimental conditions.

TABLE 2 JM96 Proposed Bits PSNR PSNR Reduction Image QP (dB) Bits (dB)Bits (%) Foreman 25 38.98 3341696 38.98 3321088 0.60 30 35.21 200306435.21 1990384 0.55 35 31.74 1189744 31.73 1184392 0.34 40 28.48 72241628.48 722264 0.11 News 25 40.12 3448504 40.13 3381512 1.94 30 35.952265968 35.96 2230296 1.57 35 31.99 1434256 31.99 1406384 1.94 40 28.40883904 28.42 875368 0.97 Silent 25 38.97 3621240 38.97 3601360 0.55 3034.97 2091720 34.96 2076720 0.81 35 31.56 1182280 31.56 1180416 0.16 4028.46 669544 28.46 672696 −0.38 Container 25 39.51 3287920 39.51 32605840.88 30 35.68 2058192 35.69 2029224 1.44 35 32.05 1247248 32.04 12190002.12 40 28.54 745848 28.54 730344 2.26 Paris 25 39.21 17437120 39.2017165032 1.56 30 34.99 11376816 34.99 11167040 1.84 35 31.10 707835231.11 6950384 1.84 40 27.50 4254824 27.52 4180808 1.61 Mobile 25 38.4227515248 38.42 27301888 0.80 30 33.75 18700976 33.74 18538960 0.89 3529.45 11923256 29.44 11821040 0.89 40 25.62 7179088 25.63 7126328 0.73Tempete 25 38.77 19968328 38.76 19748304 1.10 30 34.33 12766256 34.3312605288 1.25 35 30.30 7623776 30.30 7525136 1.28 40 26.73 4278568 26.744244224 0.82 Average 25 1.06 30 1.19 35 1.23 40 0.88

It can be seen from the Table 2 that the encoding compression rate usingthe adaptive scanning based on the intra prediction mode according tothe present invention is superior to the encoding compression rate usingthe H.264 zigzag scanning.

Meanwhile, a video compression standard to be developed following theH.264 standard is expected to use only the vertical, horizontal, DC, anddiagonal prediction modes, because the existing 9-directional intraprediction mode requires a considerable complexity. Therefore, theencoding method using the adaptive scanning of the present embodimentprovides even more improvement in the compression rate to thereby savebits about 3%.

Meanwhile, the moving picture encoding/decoding method described abovemay be authored in the form of a computer program. The codes and codesegments that form the program may be easily inferred by computerprogrammers of the art to which the present invention pertains. Also,the program is stored in a computer-readable recording medium and it canbe read and executed by a computer to realize the moving pictureencoding/decoding method. The data storage media include magneticrecording media, optical recording media, and carrier wave media.

While the present invention has been described with respect to certainpreferred embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the scope of the invention as defined in the following claims.

What is claimed is:
 1. A method of decoding motion pictures based onadaptive scanning, the method comprising: performing entropy decoding ofan encoded bitstream to obtain entropy-decoded signals; determining ascanning method for the entropy-decoded signals; recovering a picturefrom the entropy-decoded signals according to the scanning method; andoutputting the recovered picture; wherein the scanning method is anadaptive scanning method according to an intra prediction mode for theentropy-decoded signals and comprises: scanning entropy-decoded signalsof a first row with priority so that all of the entropy-decoded signalsof the first row are scanned prior to scanning entropy-decoded signalsof any other row in response to the intra prediction mode being avertical mode; and scanning entropy-decoded signals of a first columnwith priority so that all of the entropy-decoded signals of the firstcolumn are scanned prior to scanning entropy-decoded signals of anyother column in response to the intra prediction mode being a horizontalmode.
 2. The method of claim 1, wherein the method further comprisesinverse-transforming and dequantizing the entropy-decoded signals afterdetermining the scanning method for the entropy-decoded signals.
 3. Themethod of claim 1, wherein the recovering comprises first scanningentropy-decoded signals of blocks in a first row of blocks.
 4. Themethod of claim 1, wherein each of the entropy-decoded signals is atransformed and quantized residue signal that represents a differencebetween a pixel value and a predicted pixel value.